A variety of methods are known for the recovery of nickel and cobalt from lateritic ores. One method, known as the high pressure sulfuric acid leaching process, e.g., the Moa Bay process, is practiced by pulping the ore to specific mesh and solids and then selectively leaching the nickel and cobalt with sulfuric acid at elevated temperature and pressure. After proper washing and pH adjustment, the leached pulp is subjected to sulfide precipitation at elevated temperature and pressure to obtain the nickel and cobalt but not without oxidation, additional pH adjustment and selective recovery steps are performed.
The foregoing process is discussed in greater detail in a U.S. patent owned by AMAX, Inc., No. 4,044,096, which also employs a high pressure sulfuric acid leaching step of laterites at elevated temperature. The ore is first slurried and autoclaved, leached with acid and subsequently discharged into a flash tank to create turbulence.
U.S. Pat. No. 3,761,566 provides another method for leaching lateritic ores. Leaching is conducted at elevated temperature and pressure with waste solutions of ferrous sulfate.
Similarly, processes are known for the recovery of nickel and cobalt from manganese sea nodules. U.S. Pat. No. 4,085,188 provides a reductive leaching of sea nodules in an aqueous ammoniacal medium and with a reducing agent such as SO.sub.2, sulfides, NO.sub.2 or metallic iron. Manganese is reduced from its tetravelent state to manganous carbonate and, nickel, cobalt and copper are extracted.
U.S. Pat. No. 3,983,017 provides for the recovery of copper, nickel, cobalt and molybdenum from sea nodules by leaching with an aqueous ammoniacal solution containing cuprous ions. Carbon monoxide is employed as a reductant for cupric ions in order to regenerate cuprous ions for the initial leaching step.
Once metals have been solubilized they must be removed from solution in order to complete the recovery process. Recovery preferably does not consume costly materials nor does it provide useless or waste by-products. One process for the recovery of copper, silver and mercury is described in U.S. Pat. No. 3,820,979 which calls for contacting an aqueous solution of the metal with a solution of a quinonic compound in an organic solvent. After the metal precipitates and is separated, the organic phase is separated and the quinonic compound is optionally reduced for subsequent use.
Another process for the recovery of copper from acidic solutions is set forth in my U.S. Pat. No. 4,038,070 which provides for reduction of cupric ions to cuprous ions with hydrogen in the presence of a cuprous stabilizing ligand such as acetonitrile to produce cuprous-nitrile complexes that can be disproportionated to produce copper metal and cupric ions.
A similar process which employs a quinolic reductant is described in my U.S. Pat. No. 4,095,975 which also provides for the recovery of copper from acidic solutions. The copper solution is initially contacted with a quinolic reductant and an aqueous nitrile-solubilized in a water immiscible solvent to produce a nitrile stabilized cuprous solution and an organic solution of the oxidized quinolic compound. By driving off the nitrile, the cuprous ions disproportionate, producing equimolar quantities of copper metal and cupric ions. The quinolic compound can be reduced by hydrogen gas.
Notwithstanding the disclosures of the foregoing art, more economic processes for the selective extraction of desired metals such as nickel and cobalt have not appeared heretofore. Such processes should be characterized by low temperature and low pressure parameters and almost quantitative recoveries. By-products are desirably neither harmful nor costly to generate or dispose. Recycling adds to the economy and is desirably accomplished without resort to expensive reactants or processing conditions. Again, the body of art known to me has not met all of these requirements.